import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Scanner;

/**
 * Created by forcht on 2018/4/25.
 */
public class Main {

    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        String s=scanner.nextLine();
        int[] a=new int[128];
        for(int i=0;i<s.length();i++){
            char c=s.charAt(i);
            if(c>='A'&&c<='Z'||c>='a'&&c<='z'){
                a[c]++;
            }
            if(a[c]==3){
                System.out.println(c);
                break;
            }
        }
    }
}
